What are the practical consequences of rewriting Git history?

Question

Our project has been using Git for a week or so now, and we're all enjoying it a lot (using it in a tight collaborative group turns out to be quite a different Git experience). To keep things as simple as possible, we do not do any rebasing or history modifications. But we did make a few mistakes in the first week. A few commits were made that shouldn't have been done, and we managed to merge a feature branch into the wrong integration branch (1.1 instead of 1.0). And we didn't find out about these things until they were long into our history.

Now I see a lot of warnings about rewriting history, but I'm not really sure I understand the dangers involved. We use a shared bare repository, and all branches are pushed there for backup.

I would expect that if you rewrite history (say remove a commit), the full list of subsequent commits will "lose" that commit (and maybe not compile/work). I would also expect that if this happens I could actually choose to fix this at the top of history (and just leave that part of history as non-compiling).

• If I rewrite history (and everything compiles/works in all affected branches), will my co-workers need to do any special commands? (In other words, will they "know that I have done it" if I did it well?)
• Will any users with local changes that I do not know about be eligible for merge failures on git pull?
• Am I missing anything essential here?

Any references to articles/tutorials on this subject would also be really nice.

Answer 1

Required reading is Problems with rewriting history in the Git User's Manual.

If I rewrite history (and everything compiles/works in all affected branches), will my co-workers need to do any special commands (i.e. will they "know that I have done it" if I did it well?)?

They will know, and Git will tell them in no uncertain terms that something is wrong. They will get unexpected error messages, and may in the process of trying to resolve the resulting merge conflicts, inadvertently revert previous commits. This problem creates a real message, and if you're curious to see what happens you can always try it on a temporary copy of your repositories.

Will any users with local changes that I do not know about be eligible for merge failures on git pull ?

Absolutely, see above.

Am I missing anything essential here ?

Avoid rewriting history at (almost) all costs!